So-called thin-film light emitting diode chips are known in which the original growth substrate of the semiconductor layer sequence is detached and instead the semiconductor layer sequence is connected to a carrier at an opposite side relative to the original growth substrate. In this case, the radiation exit surface of the light emitting diode chip is arranged at an opposite surface of the semiconductor layer sequence relative to the carrier, that is to say at the side of the original growth substrate. In such a thin-film light emitting diode chip, it is advantageous if that side of the semiconductor layer sequence which faces the carrier is provided with a mirror layer in order that radiation emitted in the direction of the carrier is deflected in the direction of the radiation exit surface and the radiation efficiency is increased as a result.
In a thin-film light emitting diode chip, the mirror layer generally adjoins a p-type semiconductor region of the light emitting diode chip, wherein the mirror layer also serves for making electrical contact with the p-type semiconductor region. For the visible spectral range, silver is typically chosen as material for the minor layer, since silver is distinguished by high reflection in the visible spectral range.
It has been found that at the p-type contact to the silver layer during the operation of the light emitting diode chip a voltage drop of, for example, approximately 170 mV-250 mV occurs, wherein the contact resistance is approximately 5*10−3Ω cm2 to approximately 7*10−3Ω cm2.
During epitaxial growth, nitride compound semiconductors generally form a wurtzite crystal structure, the crystallographic c-axis of which runs parallel to the growth direction. Depending on the growth parameters, domains in the so-called Ga-face orientation, which corresponds to the crystallographic [0001] direction, or domains with the so-called N-face orientation, which corresponds to the crystallographic [000-1] direction, can arise in this case. Such domains can form in polar, but also in semipolar or nonpolar nitride compound semiconductors.
Nitride compound semiconductors generally have piezoelectric properties, that is to say that they have an electrical polarization even without an external electric field. The orientation of this electric field is opposite for the Ga-face orientation and the N-face orientation. For this reason, domains having Ga-face orientation and N-face orientation have different electrical properties.
The document WO 2010/045907 A1, also published as U.S. Pat. No. 8,907,359 B2, describes a contact layer system for an optoelectronic component in which a p-type contact layer composed of a nitride compound semiconductor adjoins a connection layer, wherein the p-type contact layer at an interface with the connection layer has first domains having a Ga-face orientation and second domains having an N-face orientation. Said document specifies that the area proportion of the N-face domains should preferably be between 30 percent and 60 percent in order to obtain a contact resistance that is as low as possible.